Updated at 1:15 p.m. ET

A lone gunman carrying a .45-caliber pistol killed 12 people at a country music bar in Thousand Oaks, Calif., late Wednesday, police say. When the shooting started, the Borderline Bar & Grill likely held hundreds of people, drawn by the weekly “College Country Night.”

The dead include Sgt. Ron Helus, a 29-year veteran of law enforcement who went into the nightclub within minutes of receiving an emergency call.

Police say the suspected gunman, Ian David Long, 28, was found dead inside the venue. He had previously had minor encounters with the police, Ventura County Sheriff Geoff Dean said at a news briefing Thursday morning.

Long was found dead in an office near the entrance to the club, the sheriff said, adding “We believe he shot himself” after an initial exchange of gunfire with law enforcement officers. Dean also said the shooting inside the club stopped after Helus and a highway patrol officer intervened.

When asked what the scene looked like inside the Borderline bar, Dean replied, “Like hell.”

The Borderline

Wednesday nights at the Borderline Bar & Grill are billed as Country College Night. Known for having all-ages shows, the club’s website advertises dance lessons at 9:30 and 10:30; its Facebook page shows people line dancing on its large dance floor. The Borderline is popular with students from nearby Pepperdine University, which says it has confirmed that “multiple” students were at the bar Wednesday night.

The shooting was reported at about 11:20 p.m. local time. As the gunman approached the bar, “he shot a security guard outside, and went inside and continued to fire, and killed 11 people inside,” the sheriff told NPR.

The victims who were inside the club when the shooting started seemed to range in age from 19 to 25, Dean said. As investigators worked to identify the dead, a number of families waited in anguish, having lost contact with loved ones who went to the Borderline club.

Police are still trying to determine what might have motivated Long’s actions; they don’t know why the Borderline was targeted, for instance. Some witnesses have also said the gunman used smoke bombs inside the club. Dean said his office has heard those reports but has not yet confirmed them.

When the gunman opened fire, panicked students and other patrons took shelter where they could, scrambling to hide. Many fled however they could — through windows, back doors, and fire escapes — or hid in bathrooms or the attic.

“Unfortunately, our young people, or people at nightclubs, have learned that this may happen,” Sheriff Dean said. “And they think about that. Fortunately, it probably saved a lot of lives that they fled the scene so rapidly.”

In addition to the dead, there is one other minor gunshot injury; an additional eight to 15 people were also injured inside the bar, Dean said, describing those cases as minor. Some of them left the premises on their own to go to area hospitals, he said.

Heroism Amid Deadly Violence

When sheriff’s deputies and other police arrived at the scene, they were “still hearing shots” inside, said Capt. Garo Kuredjian of the Ventura County Sheriff’s Office.

Relying on active-shooter training that emphasizes a fast response, Helus and a California Highway Patrol officer went inside the large club.

“When Sergeant Helus and the highway patrol officer went in, they immediately exchanged gunfire with the suspect and that’s when Sergeant Helus was shot several times,” Sheriff Dean said. Helus died at a nearby hospital.

“He died a hero. He went in to save lives, to save other people,” Dean said. He also said the 54-year-old sergeant had been slated to retire within the next year or so.

Dean said Helus had been on the phone with his wife when the call about the shooting came in, quickly signing off with “I love you, talk to you later.”

When the shooting started, about six off-duty officers from various agencies were inside the club, Dean said. Amid the horrific scene, he added, those officers helped to save or protect civilians.

“I’ve already talked to a parent that came up and said, ‘They stood in front of my daughter,’ ” Dean said. “So, it was amazing. It was amazing.”

The Suspected Gunman

Ian David Long lived in nearby Newbury Park. Dean says Long was armed with a Glock 21 .45-caliber pistol with an extended magazine, adding that “we don’t know if he reloaded his weapon or not.” He said Long had purchased the gun legally.

On Thursday morning, investigators requested warrants for Long’s house and for the car that he drove to the club, Dean said in a news briefing after the sun had risen over the crime scene.

The sheriff said that Long was a veteran of the U.S. Marine Corps, and that earlier this year, deputies who were called to his house were concerned he may have been suffering from post-traumatic stress disorder.

“We’ve had several contacts with Mr. Long over the years,” Dean said, “minor events such as a traffic collision; he was the victim of battery at a local bar in 2015.”

“In April of this year, deputies were called to his house for a ‘subject disturbing’ [call]. They went to the house, they talked to him; he was somewhat irate — acting a little irrationally.”

A crisis intervention team was called to the house, along with a mental health specialist, Dean said. After speaking with Long, they left the house without taking him into custody or otherwise intervening.

Witnesses described the suspect as tall and dressed all in black, wearing a hood. Both the FBI and the ATF are assisting with the case.

Inside The Club: Witness Accounts

One witness told NPR’s Nate Rott that he and others were able to escape after they grabbed a bar stool and threw it through a back window.

“I heard something go off — obviously, the gunshots,” witness Erica Sigman told NPR’s Kirk Siegler. “And I realized that it was not music very very quickly. And I heard everyone scream, ‘Get down!’ I heard people start saying, ‘Run.’ So I booked it to my car and with a group of people. … And hid behind my cars for a little bit. It stopped and then there was a second round that went off.”

Another witness told ABC 7 that he saw a suspect throw smoke bombs into the front of the restaurant and shoot a security guard.

“I was at the front door and I was talking to my stepdad. I just started hearing these big pops,” John Hedge told the station. “Pop, pop, pop. There was probably three or four, I hit the ground. I look up — the security guard is dead. Well, I don’t want to say he was dead, but he was shot. He was down. The gunman was throwing smoke grenades all over the place. I saw him point to the back of the cash register … and he just kept firing. I ran out the front door.”

Aerial footage from local news media showed a massive police response to the scene of the shooting, as multiple law enforcement agencies sent officers to help.

Reaction From The Community

The Ventura County Sheriff’s Department organized a procession to take Helus’ body from the hospital to the medical examiner’s office. The police escort began at 10 a.m. local time Thursday — and a large crowd of officials and the public turned out to show their respect and to mourn.

“He leaves behind a wife and son,” the sheriff’s department said. “Our hearts go out to his family and friends during this difficult time.”

Early Thursday, a family reunification center was set up down the highway from the Borderline, which the sheriff’s department says is staffed with chaplains and Red Cross workers.

Pepperdine University is holding classes as normal on Thursday, it says in an emergency bulletin. It adds that students can “adjust their class schedules today” if needed. The school scheduled a prayer service for the community, to be held at noon in the Smothers Theatre.

The student’s newspaper, the Pepperdine Graphic, reports that nearly 20 students were at the Borderline — and that one of them remains missing.

In addition to Pepperdine, other colleges including California State University, Channel Islands, and California Lutheran University, are located a short drive from the bar.

CSUCI President Erika D. Beck said in a statement that at least five students from the school had been at the Borderline on Wednesday. All of them, she added, had made it out safely.

This is a breaking news story. As often happens in situations like these, some information reported early may turn out to be inaccurate. We’ll move quickly to correct the record and we’ll only point to the best information we have at the time.

Copyright 2018 NPR. To see more, visit http://www.npr.org/.